class Circle{
    double radius,area;
    void setRadius(double r){
      radius = r;
    }
    double getArea(){
      area=3.14*radius*radius;
      return area;
    }
}
class Tixing {
    double above,bottom,height;
    Tixing(double a,double b,double h){ 
      above =a;
      bottom=b;
      height=h;
    }
    double getArea() {
      return (above+bottom)*height/2;
    }
}
class Student {
    double computerArea(Circle c) {
      double area = c.getArea();
      return area;
    }
    double computerArea(Tixing t) {
      double area=t.getArea();
      return area;
    }
}
public class Example4_13 {
    public static void main(String args[]) {
      Circle circle = new Circle();
      circle.setRadius(196.87);
      Tixing lader = new Tixing(3,21,9);
      Student zhang = new Student();
      System.out.println("zhang计算圆的面积:");
      double result = zhang.computerArea(circle);
      System.out.println(result);
      System.out.println("zhang计算梯形的面积:");
      result = zhang.computerArea(lader); 
      System.out.println(result);
   }
}
